1. Field of the Invention
This invention relates generally to magnetic recording and reproducing apparatus, such as, video tape recorders of the helical scan type, and more particularly is directed to apparatus of such type capable of improved operation in various reproducing modes, such as, still-motion, slow-motion and quick-motion reproducing modes.
2. Description of the Prior Art
In existing helical scan video tape recorders, the successive parallel tracks in which the video signal is recorded on the magnetic tape are each at a fixed angle to the longitudinal or driven direction of the tape, with such angle being determined by the angle at which the tape is guided about the guide drum having a rotary magnetic head or heads associated therewith, the speed of rotation of such head or heads, and the speed at which the tape is longitudinally driven. If, during reproducing, the speed at which the tape is driven is made to be equal to the standard tape speed for recording, then the scanning path of movement of each rotary head can be made to accurately coincide with a respective one of the record tracks for properly reproducing the video signal recorded therein.
However, if the tape is driven at an arbitrary speed during reproducing, which arbitrary speed is different from the standard speed used for recording, for example, as when the tape is a rest during still-motion reproducing, then the path along which each rotary head repeatedly scans the tape will deviate angularly from the direction along the record tracks. Similarly, when the reproducing operation is carried out with an arbitrary tape speed which is less than, or greater than the standard tape speed for recording, as during slow-motion, or quick-motion reproducing, respectively, the scanning path of each head will deviate angularly from the direction along the tracks. In order to avoid such angular deviation of the head scanning path or locus from the direction along the tracks, it has been proposed to mount each rotary head by means of an electro-mechanical transducer, for example, a bi-morph leaf, which is effective, in response to an electrical drive signal, to displace the respective rotary head in directions generally transverse to the direction along the tracks, and to apply to the bi-morph leaf a suitable drive signal, for example, having a sawtooth wave component with a period corresponding to the time required for the respective rotary head to scan along each of the tracks, so as to compensate for the previously mentioned angular deviation of the scanning path from the direction along the tracks.
In the case where the tape speed during reproducing is selected to be a fraction of the standard tape speed for recording, so as to establish a slow-motion reproducing mode, each rotary head effects a plurality of scans across the tape in the time required for the tape to move longitudinally a distance equal to the pitch of the successive record tracks. In order to ensure that each head will precisely scan along a record track during each of the repeated scans of the tape during slow-motion reproducing, it has been proposed that the drive signal applied to the bi-morph leaf supporting each head should include the previously mentioned sawtooth wave component and also a component which varies stepwise for the successive scans.
It has also been proposed to effect the recording of the video signal in successive parallel tracks with so-called H-alignment, that is, with the horizontal synchronizing signals, as recorded in adjacent tracks, being located at positions that are aligned with each other in the transverse direction relative to the direction along the tracks, so that interference due to cross-talk between the signals recorded in adjacent tracks is reduced even when the path or locus of a head scanning one of the tracks deviates somewhat from that one track.
Although the above generally-described conventional procedures can reduce or avoid the variations in level of the reproduced video signal that would otherwise be caused by deviation of the scanning path of the head from the record track when reproducing with an arbitrary tape speed other than the standard tape speed for recording, such conventional procedures have not been effective to avoid disturbance of the horizontal synchronizing signals, particularly at the joining parts of fields which are contiguous or mutually adjacent in point of time. By reason of the foregoing, in the image or picture resulting from the reproduced video signal in the still-motion, slow-motion or quick-motion mode, the lateral location at which the final scan of one field is seen to terminate at the bottom of the raster will not correspond with the lateral location at which the initial scan of the next field is seen to commence at the top of the raster. Even if compensating circuits are capable of correcting such lateral deviations between the locations of termination and commencement of the last and first scans of successive fields, the result thereof is a swaying of the image which is visually disturbing.